The present invention relates to a brake booster for motor vehicles comprising a booster housing, the interior space of which is subdivided by a movable wall into a low-pressure chamber and a working chamber, and with a control housing that carries the movable wall, in which a control valve is arranged which controls a pneumatic pressure difference acting on the movable wall and is operable both by an actuating rod by means of a valve piston and, irrespective of the actuating rod, by an electromagnet, the said control valve being comprised of three sealing seats which are arranged concentrically to one another and of a valve body, which cooperates with the sealing seats and is furnished with axial passages, with the first sealing seat being provided in the control housing and the second sealing seat being provided on the valve piston, while the third sealing seat is provided on a sleeve that cooperates with the electromagnet, and with a ring being arranged so as to be displaceable in relation to the third sealing seat, said ring being supported on the sleeve by the intermediary of an elastic valve body or compressible element, the fringe area of the element close to the valve body including contact areas that are separated by radial apertures, and which is arranged in the release position axially offset towards the valve body with regard to the third sealing seat.
EP 0 866 758 B1 discloses a brake booster of this type. In the prior art brake booster, however, the radial distance between the second sealing seat provided at the valve piston and the third sealing seat is very small, so that the air flow cross-sections are greatly affected, impairing the dynamics of the desired control as well as its quality.
In view of the above, an object of the invention is to disclose measures avoiding the above-mentioned negative influence to the largest degree possible. Another objective is to improve the sound behavior of the brake booster.